(www.bostonglobe.com) The pending closure of the Vermont Yankee nuclear power station is the latest in a string of planned plant retirements that many industry analysts say forecast a shrinking role for nuclear in the nation’s energy mix. Vermont Yankee, which began operating in 1972, is the fifth reactor in the country to be scheduled for closure over the past year, dealing another blow to industry hopes of a nuclear renaissance. While four new reactors are scheduled to come online over the next several years, analysts expect more nuclear plants to shut down, unable to compete with natural gas and renewable sources such as wind and solar. Entergy Corp., the Louisiana company that owns Vermont Yankee, said on Tuesday that it would shut down the 41-year-old plant.